NICHD is evaluating adolescent injury causes, violence, and related behaviors through participation with the World Health Organization Study of Health Behavior in School Children (WHO-HBSC). The study addresses the hypothesis that U.S. youth may have adopted lifestyles that place them at greater risk for certain health problems than their counterparts in other nations. The WHO-HBSC is used to monitor and investigate patterns, determinants and effects of health related behaviors. International comparisons test the degree to which such behavior is a natural and inevitable part of current adolescent development. Analysis of differences and similarities will be conducted to help identify influential factors included family, school and peers. Multiple and different cross-national comparisons are a feature of this study that allows analysis and hypotheses testing of policy differences, cultural differences and natural experiments. The Epidemiology Branch collaborated with the Center for Research on Mothers and Children (NICHD) toperform the first full surveys as required for participation in the WHO collaboration. The WHO coordinates a quadrennial survey that compares health behavior in adolescents in 30 countries. Data from the 1996 preliminary survey have been presented in international conferences and are under analysis. NICHD and other countries completed the full survey by June 1998. International comparisons of various health behaviors in 30 countries show that the U.S. ranks 14th in medically attended injuries but in first and second place for injuries occurring in homes and schools respectively. The U.S. students rank higher than most countries in both prevalence and use of medications for headaches, stomach aches, and backaches. Girls report a higher frequency of problems than boys.